Similar themes, such as alchemy, and the time era. Though the style it's shown in is quite different, as well as FMA having a main character (as opposed to Baccano), they're still similar in many ways. Both having a wide range of characters, violence, and nicely animated action.

Both of these series are set around the early 1900's. The practice of alchemy is within them both, however one more so than the other (Fullmetal Alchemist). Also the idealogy of immortality is brought up quite a bit in both. They may not be eerily similar, but they do have a similarity in overall feeling.

They both involve alchemy and homunculi, and have fighting scenes. Both animes have humor in it, and are set in similar time periods. They share many themes as well, so if you enjoy supernatural things and characters with strong individual personalities, you'll enjoy it!